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BIOL 404 > Article 4 > Flashcards

Article 4 Flashcards

1
Q

what are taste buds, and where are they located?

A

specialized sensory organs located in the tongue and palate epithelium

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2
Q

how do taste buds transmit taste information to the brain?

A

via afferent gustatory nerves

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3
Q

name the 5 taste modalities that most mammals can detect

A

sweetness, bitterness, saltiness, sourness and umami

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4
Q

what is umami and what is it associated with?

A

meaty or savory taste and is associated with compounds like monosodium L-glutamate (MSG)

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5
Q

how can taste-perception mechanisms be categorized?

A

those involving ion channels and those involving GPCRs

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6
Q

where are GPCRs located in taste buds and what do they detect?

A

in the apical membrane of type II taste buds (TBCs) and they detect sweet, umami and bitter compounds

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7
Q

describe the signal-transduction cascade triggered by GPCR activation

A

GPCR activation triggers a signal transduction involving the activation of heterotrimeric G proteins, phospholipase C-b2 (PLCB2), production of inostiol 1,4,5-trisphosphate (InsP3) and InsP3-dependent Ca2+ release from the ER

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8
Q

what is the role of TRMP5 channels in taste perception?

A

are activated in response to increased intracellular calcium and lead to membrane depolarization, which is essential for generating taste signals

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9
Q

how does neurotransmitter release occur in Type II taste bud cells, and what is unique about it?

A

involves an ion channel mechanism rather than classical vesicular exocytosis. they lack classical synaptic structures like synaptic vesicles

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10
Q

what is the role of CALHM1 in the ATP-release channel mechanism?

A

responsible for releasing ATP in response to taste events

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11
Q

how does the absence of CALHM1 impact the perception of taste compounds?

A

taste compounds fail to stimulate ATP release, resulting in the loss of perception of GPCR-mediated tastes

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12
Q

what are the notable differences in activation kinetics between CALHM1 channels and the NT-release channels?

A

CALHM1 have slower activation kinetics in xenopus compared to the rapid Na+ action potentials that trigger ATP release in taste bud cells

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13
Q

How does CBX affect ATP release in taste bud cells and how does it relate to CALHM1?

A

ATP release by type II taste buds can be inhibited by CBX, which inhibits nonspecific pannexin-1 and connexin hemichannel. CALHM1 currents in Xenopus are not affected by CBX

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14
Q

Initially, what role were pannexins thought to play in ATP release, and what does recent evidence suggest about their involvement

A

Pannexins were initially considered potential contributors to ATP release in taste bud cells. However, recent evidence indicates that they are not involved in this specific process.

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15
Q

what is CALHM1 and what are its properties?

A

CALHM1 is a protein that forms ion channels in cells. These channels can be opened or closed by changes in cell voltage and calcium ions. They have a wide pore and allow various ions, including calcium and ATP, to pass through.

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16
Q

what is the CALHM gene family and where are its homologs found?

A

initially known as the FAM26 gene family, is present in vertebrates. CALHM1 homologs are absent in yeast and drosph but exist in c elegans

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17
Q

What is the significance of CALHM1 homolog clhm-1 in Caenorhabditis elegans?

A

When clhm-1 is expressed in a different system, it behaves similarly to human and mouse CALHM1 in terms of ion permeation and voltage dependence.

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18
Q

What is CALHM3, and where is it enriched?

A

CALHM3 is another homolog of CALHM1. It is enriched in type II taste bud cells.

19
Q

Does CALHM3 function as an ion channel by itself?

A

No, CALHM3 alone does not create ion currents.

20
Q

What happens when CALHM1 and CALHM3 come together?

A

When CALHM1 and CALHM3 come together, they form a hexameric ion channel with specific properties.

21
Q

What is the role of CALHM1/CALHM3 channels in taste perception?

A

CALHM1/CALHM3 channels have properties matching the ATP-release channel in type II taste bud cells. They are responsible for releasing ATP and transmitting taste information for sweet, umami, and bitter tastes.

22
Q

What are the consequences of deleting the Calhm3 gene?

A

Deleting the Calhm3 gene eliminates certain ion currents and the release of ATP in response to taste stimuli. However, it does not affect cell excitability or Calhm1 expression.

23
Q

what triggers the ATP release in type II TBCs

A

APs

24
Q

why is CALHM1 considered insufficent to be the sole ATP-release channel?

A

activation kinetics are too slow to be activated by APs

25
Q

what were researchers investigating regarding CALHM1 homologs?

A

whether CALHM2 and CALHM3 are functional ion channels

26
Q

what were the results of expressing CALHM1 in xenopus oocytes?

A

generated voltage-gated currents, but these currents had slow activation kinetics

27
Q

how did CALHM2 and CALHM3 behave when expressed alone in xenopus oocytes?

A

failed to generate functional plasma membrane channels

28
Q

what happened when CALHM3 was expressed w CALHM1?

A

resulted in large currents with faster activation kinetics and shifted the voltage at which the channels activate to more negative values

29
Q

Did CALHM1+CALHM3-expressing Xenopus oocytes retain sensitivity to extracellular calcium ions (Ca2+o)?

A

Yes, currents in CALHM1+CALHM3-expressing Xenopus oocytes remained sensitive to extracellular calcium ions (Ca2+o).

30
Q

what were the researchers investigating in mammalian cells (N2a cells)?

A

the impact of CALHM isoforms on ion channel properties in N2a mouse neuroblastoma cells

31
Q

how does expression CALHM3 with CALHM1 affect the currents in N2a?

A

enhances voltage-activated current density, shifts the conductance-voltage relationship to more negative voltage, and accelerates voltage-dependent activation kinetics

31
Q

what happens when CALHM1 is expressed in N2a cells?

A

generates small and slowly activating voltage-gated channels

32
Q

does CALHM3 alter the relative permeabilities of different ions when co-expressed with CALHM1?

A

CALHM3 does not significantly affect the relative permeabilities of calcium, sodium, potassium, and chloride ions when co-expressed with CALHM1

33
Q

what happens to ATP release when CALHM3 is expressed alone or with CALHM1 in HeLa cells?

A

CALHM3 alone does not promote ATP release, but it enhances CALHM1-mediated ATP release in HeLa cells.

34
Q

What does the similarity in activation kinetics of CALHM1+CALHM3 currents in N2a cells suggest?

A

suggests that CALHM1+CALHM3 currents could be activated by action potentials, although CALHM proteins lack obvious voltage-sensing domains.

35
Q

how did researchers determine whether CALHM1 and 3 interact in a single ion channel complex?

A

used heterologous expression in n2a cells

36
Q

What was observed when CALHM1 and CALHM3 were co-expressed in N2a cells regarding their co-localization?

A

CALHM1 and CALHM3 co-localized within the cells when co-expressed in N2a cells.

37
Q

What did immunoprecipitation experiments reveal about the interaction between CALHM1 and CALHM3?

A

Immunoprecipitation of one CALHM homolog co-precipitated the other, indicating that CALHM1 and CALHM3 interact at the molecular level.

38
Q

Was the interaction between CALHM1 and CALHM3 specific to these proteins, or did it involve other membrane proteins?

A

was specific to CALHM1 and CALHM3 and did not involve other membrane proteins, such as Panx-1.

39
Q

What effect did co-expression of CALHM3 have on the localization of CALHM1?

A

Co-expression of CALHM3 enhanced the plasma membrane (PM) localization of CALHM1.

40
Q

How was the mutual promotion of plasma membrane (PM) localization of CALHM1 and CALHM3 confirmed?

A

Surface biotinylation of PM proteins confirmed that co-expressed CALHM1 and CALHM3 mutually promoted their localization to the plasma membrane (PM).

41
Q

What may explain the larger currents observed in N2a cells co-expressing CALHM1 and CALHM3?

A

The interaction and mutual promotion of PM localization between CALHM1 and CALHM3 may explain the larger currents observed in N2a cells co-expressing both homologs.

42
Q

what type of channel complex does CALHM1 form when expressed alone?

A

homo-hexameric channel

43
Q
A

BIOL 404 (20 decks)

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